This project aims to validate a novel neurophysiological assessment tool for Attention-Deficit/Hyperactivity Disorder (ADHD). Adult ADHD is prevalent and enduring and the objective methods for assessment of the disorder are limited, particularly based on functional neurophysiological indices that can also be made readily and inexpensively accessible to a wide market. An important aspect of ADHD would appear to be difficulty in the maintenance of attentional control over periods of 10s of seconds, manifesting as inconsistent within-individual performance on sustained attention tasks with periods of normal performance and other periods of poor performance. We have created an innovative assessment tool, the Neurophysiological Attention Test (NAT), that tracks sustained attention based on electroencephalography (EEG). The NAT provides critical new measures of the fluctuations in control. Unlike any other behavioral or EEG-based assessment tools, the NAT enables continuous tracking of infra-slow fluctuations (ISFs) in neurophysiological indices of BOTH attending targets and ignoring distractors simultaneously, two core components of attention control, during sustained attention tasks (patent pending). Phase-I results show that the NAT identifies both behavioral and EEG indicators that successfully discriminate individuals with ADHD from healthy comparison individuals, and that correlate with scores on rating scales widely used to characterize the inattentive and impulsive features of ADHD. The proposed Phase II project will extend our work from Phase I to further improve the stimulus parameters, optimize the EEG measures for differentiating adults with ADHD from controls, test these improvements in a larger clinical trial (120 subjects per group) conducted across three sites to expand the sample size and verify utility under different recording conditions, and will determine the minimal number of EEG sensors needed for further development of the device. Ultimately, it is expected that the NAT will be an inexpensive, easy to use, easy to distribute, EEG-based objective assessment instrument that provides behavioral measures and functional neurophysiological biomarkers for ADHD. Future uses of the NAT include informing diagnosis, monitoring treatment, evaluating new treatments, and clinical research on the brain mechanisms of ADHD that may lead to better brain-based models and treatment options.